In object sensing systems, including but not limited to touch capacitance sensing systems, linearity and accuracy are desirable responses. Accuracy can be the difference between an actual object position (e.g., finger touch location) and a location reported to a system (e.g., location on a touch display). Linearity can be the straightness of a linear path over sensor region (e.g., line drawn on a panel surface).
Conventionally, object sensing systems can have reduced linearity and accuracy at the edges of a sensing area (including corners). In some conventional approaches, a “curvature” of a sensing signal (caused by the object passing off the edge) was determined, and then compensated for when an object was at an edge location. Such compensation could include generating values for “virtual sensors” corresponding to regions beyond the edge.
A drawback to such conventional approaches can arise when sensed objects vary in shape. In particular, in capacitance sensing touch systems, contacting finger shapes may vary (i.e., can be various oval shapes), while tested shapes (used to compensate for curvature) can have a uniform shape (i.e., be circular). Further, such conventional approaches can constantly determine finger size and or shape while determining position. At edge locations, it can be difficult to accurately determine finger size. Consequently, a touch response can exhibit a “scalloping” response at edge locations (poor linearity) and/or jumps in finger size, which can result in poor accuracy.